JP 2004338750 A and JP 2004242944 A describe infusion bags which are made of spunbonded nonwoven made of core/sheath fibers having a high-melting core component and a low-melting sheath component. The high-melting core component is made of a polyester, in particular polyethylene terephthalate; the low-melting sheath component is made of polypropylene or polyethylene. The low-melting sheath component is responsible for the hot sealability of the material.
Infusion bags of the above-mentioned type, which are made of dual-layer textile fabric, are currently being offered on the market. One layer is responsible for the filtering properties such as particle retaining capability, water permeability, and permeability for the extracted active substances, as well as for the mechanical strength. The second layer is used for the hot sealability of the textile fabric and is made of fibers of thermoplastic polymers, in particular of polyethylene and polypropylene.
The disadvantage of the known infusion bags is their higher manufacturing complexity, higher manufacturing costs due to the spinning and applying of the second layer, the low transparency due to the dual-layer structure, the lower melting points of the fabrics in the second layer, in particular of polyethylene and polypropylene, which may result in conglutination at the cut edges during the manufacture of the base material.